The present disclosure relates to digital image processing technologies.
As digital image processing apparatuses become popular and widely used, an auto white balance (AWB) function has been used to process digital image signals. The AWB function is performed on the color of a white subject by automatically adjusting red (R), green (G) and blue (B) gains so as to maintain a color temperature constant, that is, to obtain an electrical achromatic color in an area having high brightness or low brightness. The AWB function may be realized by various methods. For example, the AWB function may be realized by integrating image signals input through a charge-coupled device (CCD) over the whole image in which auto exposure (AE) is completely processed.
In a conventional method of adjusting AWB an optical image signal output from a subject via a lens is photoelectrically transformed through a CCD. The photoelectrically transformed optical image signal is stored on an image-by-image basis or a frame-by-frame basis in a memory such as dynamic random access memory (DRAM). The conventional method of adjusting AWB uses a technology of integrating input values of the CCD over the whole image to obtain an achromatic color, and a R/G and B/G coordinates system is used as a color coordinates system with respect to a color temperature. When the whole image is integrated to determine a color indicated by the color temperature, the brightest and darkest portions may saturate or distort the whole image, and thus the brightest and darkest portions are excluded.
A mosaic CCD exhibits a single color in units with a size of 2×2 pixels. Thus, image signals stored in a memory are integrated over the whole image in units with a size of 2×2 pixels. The brightest and darkest portions of the whole image are excluded by performing clipping thereon, and gains are calculated only on available portions. Then, the whole image is divided on a predetermined pixel-sized on a block-by-block basis, and light sources are detected for all blocks. An AWB process is performed on the detected light sources, and then the obtained AWB gains are applied to the whole image.
The given digital image processing apparatuses have used the same method of adjusting AWB throughout the world by using an AWB algorithm based on AWB parameters that are used when the apparatuses are mass-produced. That is, AWB performance has been optimized using a standard scene and a standard chart that are supported by each company, without consideration of information regarding a location being photographed and a time of photographing. However, color temperatures are different according to the location being photographed and the time of photographing. Thus, although the same subject is photographed, colors in the pictures are different in terms of color recognition according to the location being photographed and the time of photographing. When the given digital cameras perform photography at a location that differs from the standard scene and chart supported by each company, it is difficult to obtain the optimized AWB performance with respect to the given location and time.